In recent years, active development of robots cooperating with workers has been observed because of increase in cell production plants and the like. Unlike those conventional robots operating in areas separated from workers' areas, these robots cooperating with workers need to share the work areas with the workers. Accordingly, specifications required to these cooperative robots are different from the conventional industrial robots and the like.
Firstly, a conventional industrial robot includes an electric motor or a decelerator, and achieves high accuracy in positioning a hand such as repeatability of about 0.1 mm by feedback control with high gain. However, a mechanism driven by such an electric motor is highly rigid with poor flexibility in many cases, which is problematic in terms of safety.
To the contrary, safety is quite important to a robot cooperating with a worker so as not to hurt the worker by contact with each other. Therefore, such a mechanism driven by the electric motor as in the conventional industrial robot is unsuited to domestic robots and the like in the fields in which safety is highly required, and there is a need for flexible and safe robot arms.
In order to solve the problems, there has been proposed a robot arm that includes a pneumatic actuator of Mckibben type, for example. The pneumatic actuator of Mckibben type is configured such that a restraint part made of fiber cords is provided on an outer surface of a tubular elastic body made of a rubber material, and respective ends of the tubular elastic body are hermetically sealed by sealing members. When an internal pressure is applied to an inner space of the tubular elastic body with use of a compressive fluid such as air through a fluid injection/ejection part, the tubular elastic body tends to expand mainly in a radial direction. However, the restraint part functions to convert the radially expanding motion to a motion along a center axis of the tubular elastic body. As a result, the tubular elastic body is contracted in the entire length. This Mckibben type actuator is mainly configured by an elastic body, and is thus characterized by being flexible, safe, and light in weight.
Secondly, the conventional industrial robot operates in the area separated from the workers' area. Accordingly, safety is considered to be most preferably achieved by immediately stopping the robot in case of malfunction of a sensor or the like.
To the contrary, with a robot operating in the workers' area, it is not always safest to immediately stop the robot in case of malfunction of a sensor or the like. For example, even when the robot cooperating with a worker suddenly stops, the cooperative worker may be unable to immediately stop and thus may be in danger. However, when the sensor is in trouble, it is impossible to obtain information necessary for operation control. Therefore, it is difficult to operate the robot continuously.
In order to cope with such malfunction of a sensor, there has been disclosed, as a conventional technique, a control apparatus that controls a robot by reading data preliminarily instructed and stored, instead of a sensor signal (Patent Literature 1). There has been also disclosed a shift control apparatus for use in a robot including a distance sensor and a plurality of shift mechanism position detectors, the shift control apparatus including a computing unit that obtains an alternative signal same as a correct shift mechanism position signal to be originally transmitted from a broken shift mechanism position detector, from a sensor signal from the distance sensor and a shift mechanism position signal from the normal shift mechanism position detector (Patent Literature 2).